Fan and low pressure compressor geared to low speed spool of gas turbine engine

ABSTRACT

A gas turbine engine may include a high speed spool, a low speed spool, a first epicyclic gear system, and a second epicyclic gear system. Generally, the high speed spool mechanically connects a high pressure turbine to a high pressure compressor, and the low speed spool mechanically connects a low pressure turbine to at least one of a fan and a prop via the first epicyclic gear system and to a low pressure compressor via the second epicyclic gear system, according to various embodiments. The first epicyclic gear system and the second epicyclic gear system may include a common sun gear shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent applicationSer. No. 62/780,622, filed on Dec. 17, 2018, the entire contents ofwhich are incorporated herein by reference in their entirety.

FIELD

The present disclosure relates to gas turbine engines, and morespecifically to fan and low pressure compressor configurations of gasturbine engines.

BACKGROUND

Conventional two-spool gas turbine engines (e.g., two-spool turbofanengines) typically include a low pressure compressor configured to berotated by a low pressure turbine via a low speed spool, and a highpressure compressor configured to be rotated by a high pressure turbinevia a high speed spool. Conventional efforts to optimize efficiency andmaximize power include mechanically connecting the low pressurecompressor to the low speed spool via a gearbox while the fan isdirectly driven off of the low speed spool. However, such conventionalarchitectures may require a large low pressure turbine and may limit thebypass ratio of the gas turbine engine.

SUMMARY

In various embodiments, the present disclosure provides a gas turbineengine that includes a high speed spool, a low speed spool, a firstepicyclic gear system, and a second epicyclic gear system. Generally,the high speed spool mechanically connects a high pressure turbine to ahigh pressure compressor, and the low speed spool mechanically connectsa low pressure turbine to at least one of a fan and a prop via the firstepicyclic gear system and to a low pressure compressor via the secondepicyclic gear system, according to various embodiments.

In various embodiments, the first epicyclic gear system and the secondepicyclic gear system comprise a common sun gear shaft. For example, thecommon sun gear shaft may be a section of the low speed spool, and mayinclude a first portion that is forward of a second portion, wherein thefirst portion is mechanically connected to the first epicyclic gearsystem and the second portion is mechanically connected to the secondepicyclic gear system. In various embodiments, the first and secondportions of the common sun gear shaft may have the same radius, or mayhave different radiuses. That is, the first portion of the common sungear shaft (e.g., the first sun gear) may have a different radius thanthe second portion of the common sun gear shaft (e.g., the second sungear).

In various embodiments, the first epicyclic gear system and the secondepicyclic gear system are mounted to a common static support structure.In various embodiments, the at least one of the fan and the prop and thelow pressure compressor are mounted to a common static supportstructure. In various embodiments, the first epicyclic gear system, thesecond epicyclic gear system, the at least one of the fan and the prop,and the low pressure compressor are all mounted to a common staticsupport structure.

In various embodiments, the common static support structure is parallelto an engine central longitudinal axis of the gas turbine engine. Thecommon static support structure may be mounted to a structural case aftof both the at least one of the fan and the prop and the low pressurecompressor, but forward of the high pressure compressor. In variousembodiments, the at least one of the fan and the prop is the fan, andthe fan and the low pressure compressor are configured to rotate in asame direction. In various embodiments, the fan and the low pressurecompressor are configured to rotate in opposite directions.

In various embodiments, the first epicyclic gear system is aplanetary-type system. In such embodiments, the first epicyclic gearsystem may include a gear carrier mounted to intermediate gears, and thefan may be coupled to the gear carrier. In various embodiments, thesecond epicyclic gear system is a star-type system. In such embodiments,the second epicyclic gear system may include a rotating ring gear, andthe low pressure compressor may be coupled to the rotating ring gear.

Also disclosed herein, according to various embodiments, is a method ofoperating a gas turbine engine, the method comprising operating at leastone of a fan and a prop at a first operating speed and operating a lowpressure compressor at a second operating speed. In various embodiments,the at least one of the fan and the prop and the low pressure compressorare mechanically connected to a low speed spool of the gas turbineengine via a first epicyclic gear system and a second epicyclic gearsystem, respectively.

The forgoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated hereinotherwise. These features and elements as well as the operation of thedisclosed embodiments will become more apparent in light of thefollowing description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a typical gas turbine engine, inaccordance with various embodiments;

FIG. 2A is a cross-sectional view of a gas turbine engine having ageared fan and a geared low pressure compressor, in accordance withvarious embodiments;

FIG. 2B is a magnified view of a portion of the gas turbine engine ofFIG. 2A, in accordance with various embodiments;

FIG. 3 is a cross-sectional view of a portion of a gas turbine engine,in accordance with various embodiments;

FIG. 4 is a cross-sectional view of a portion of a gas turbine engine,in accordance with various embodiments; and

FIG. 5 is a schematic flow chart diagram of a method of operating a gasturbine engine, in accordance with various embodiments.

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration. While these exemplary embodiments are described insufficient detail to enable those skilled in the art to practice thedisclosure, it should be understood that other embodiments may berealized and that logical changes and adaptations in design andconstruction may be made in accordance with this disclosure and theteachings herein without departing from the spirit and scope of thedisclosure. Thus, the detailed description herein is presented forpurposes of illustration only and not of limitation.

Disclosed herein, according to various embodiments, is a gas turbineengine that uses two epicyclic gear systems driven off of the low speedspool of the gas turbine engine to drive the fan and the low pressurecompressor, respectively. With both the fan and the low pressurecompressor being geared off of the low speed spool, the operating speedof the fan and the low pressure compressor can be independentconfigured/optimized in order to improve the operating efficiency of atwo-spool gas turbine engine.

In various embodiments and with reference to FIG. 1, a typical gasturbine engine 20 is provided. Gas turbine engine 20 may be a two-spoolturbofan that generally incorporates a fan section 22, a compressorsection 24, a combustor section 26 and a turbine section 28. Inoperation, fan section 22 can drive fluid (e.g., air) along a bypassflow-path B while compressor section 24 can drive fluid along a coreflow-path C for compression and communication into combustor section 26then expansion through turbine section 28. Although depicted as aturbofan gas turbine engine 20 herein, it should be understood that theconcepts described herein are not limited to use with turbofans as theteachings may be applied to other types of turbine engines includingthree-spool architectures.

Typical gas turbine engines 20 generally comprise a low speed spool 30and a high speed spool 32 mounted for rotation about an engine centrallongitudinal axis A-A′ relative to an engine static structure 36 orengine case via several bearing systems 38, 38-1, and 38-2. Enginecentral longitudinal axis A-A′ is oriented in the z direction (axialdirection) on the provided xyz axis. The y direction on the provided xyzaxis refers to radial directions and the x direction on the provided xyzaxis refers to the circumferential direction. It should be understoodthat various bearing systems 38 at various locations may alternativelyor additionally be provided, including for example, bearing system 38,bearing system 38-1, and bearing system 38-2.

Low speed spool 30 may generally comprise an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. As described in greater detail below with reference to theremaining figures, the fan 42 and the low pressure compressor 44 may begeared to the low speed spool 30. High speed spool 32 may comprise anouter shaft 50 that interconnects a high pressure compressor 52 and highpressure turbine 54.

A combustor 56 may be located between high pressure compressor 52 andhigh pressure turbine 54. The combustor section 26 may have an annularwall assembly having inner and outer shells that support respectiveinner and outer heat shielding liners. The heat shield liners mayinclude a plurality of combustor panels that collectively define theannular combustion chamber of the combustor 56. An annular coolingcavity is defined between the respective shells and combustor panels forsupplying cooling air. Impingement holes are located in the shell tosupply the cooling air from an outer air plenum and into the annularcooling cavity.

A mid-turbine frame 57 of engine static structure 36 may be locatedgenerally between high pressure turbine 54 and low pressure turbine 46.Mid-turbine frame 57 may support one or more bearing systems 38 inturbine section 28. Inner shaft 40 and outer shaft 50 may be concentricand rotate via bearing systems 38 about the engine central longitudinalaxis A-A′, which is collinear with their longitudinal axes. As usedherein, a “high pressure” compressor or turbine experiences a higherpressure than a corresponding “low pressure” compressor or turbine.

The core airflow C may be compressed by low pressure compressor 44 thenhigh pressure compressor 52, mixed and burned with fuel in combustor 56,then expanded over high pressure turbine 54 and low pressure turbine 46.Turbines 46, 54 rotationally drive the respective low speed spool 30 andhigh speed spool 32 in response to the expansion.

In various embodiments, and as described in greater detail below, boththe fan and the low pressure compressor may be mechanically connected tothe low speed spool using a geared architecture, such as an epicyclicgear system. The geared architecture may have a gear reduction ratio ofgreater than about 2.3 and low pressure turbine 46 may have a pressureratio that is greater than about five (5). In various embodiments, thebypass ratio of gas turbine engine 20 is greater than about ten (10:1).In various embodiments, the diameter of fan 42 may be significantlylarger than that of the low pressure compressor 44, and the low pressureturbine 46 may have a pressure ratio that is greater than about five(5:1). Low pressure turbine 46 pressure ratio may be measured prior toinlet of low pressure turbine 46 as related to the pressure at theoutlet of low pressure turbine 46 prior to an exhaust nozzle. It shouldbe understood, however, that the above parameters are exemplary ofvarious embodiments of a suitable geared architecture engine and thatthe present disclosure contemplates other gas turbine engines includingdirect drive turbofans. A gas turbine engine may comprise an industrialgas turbine (IGT) or a geared aircraft engine, such as a gearedturbofan, or non-geared aircraft engine, such as a turbofan, or maycomprise any gas turbine engine as desired.

Disclosed herein, in accordance with various embodiments and withreference to FIGS. 2A and 2B, is a gas turbine engine 100 having a lowspeed spool 130 and a high speed spool 132, with a fan 142 beingmechanically connected to the low speed spool 130 via a first epicyclicgear system 110 and a low pressure compressor 144 mechanically connectedto the low speed spool 130 via a second epicyclic gear system 120. Thus,the gas turbine engine described below throughout the remainder of thisdisclosure may differ from the gas turbine engine 20 shown and describedabove with reference to FIG. 1 because both the fan 142 and the lowpressure compressor 144 (FIG. 2) are driven/rotated by the low speedspool 130 via first and second epicyclic gear systems 110, 120,respectively.

In various embodiments, the high speed spool 132 of the gas turbineengine 100 mechanically connects a high pressure turbine 154 to a highpressure compressor 152. Still further, the gas turbine engine 100 mayinclude an engine case 136 and a combustor 156 disposed between the highpressure compressor 152 and the high pressure turbine 154. As usedherein, the phrase “mechanically coupled” or “mechanically connected”means connected, whether directly or indirectly, in power-transferringcommunication via mechanical components structures (gears, shafts,etc.). Also, while numerous details are included herein pertaining to afan of a gas turbine engine, a similar configuration may be employed foran engine that includes a prop (instead of a fan) that is forward of alow pressure compressor.

In various embodiments, by mechanically coupling both the fan 142 andthe low pressure compressor 144 to the low speed spool via respectiveepicyclic gear systems 110, 120, improved operational efficiency may beachieved because the speeds of the fan 142 and the low pressurecompressor 144 may be independently configured, and may be differentfrom the speed of the low speed spool 130. That is, the gas turbineengine 100 may be enabled to operate with improved efficiency and/orwith improved power because the relative operating speeds of the fan142, the low pressure compressor 144, and the low speed spool 130 may beindependently configured based on expected operating/use parameters.

In various embodiments, and with reference to FIG. 2B, the low speedspool 130 has a forward section or a forward portion that defines acommon sun gear shaft 135 for both the first and second epicyclic gearsystems 110, 120. That is, the low speed spool 130 may comprise aportion or section (e.g., common sun gear shaft 135) that defines or ismechanically coupled to both a first sun gear 111 of the first epicyclicgear system 110 and a second sun gear 121 of the second epicyclic gearsystem 120. Each of the epicyclic gear systems 110, 120 includes aplurality of intermediate gears 112, 122, a gear carrier 113, 123, and aring gear 114, 124. More specifically, the first epicyclic gear system110 includes a first sun gear 111, a first plurality of intermediategears 112, a first gear carrier 113, and a first ring gear 114 and thesecond epicyclic gear system 120 includes a second sun gear 121, asecond plurality of intermediate gears 122, a second gear carrier 123,and a second ring gear 124, according to various embodiments. Generally,each gear carrier 113, 123 is coupled to a respective plurality ofintermediate gears 112, 122, and each plurality of intermediate gears112, 122 is disposed between the respective sun gear 111, 121 and therespective ring gear 114, 124.

In various embodiments, and with continued reference to FIG. 2B, thefirst sun gear 111 has the same radius as the second sun gear 121. Invarious embodiments, the first epicyclic gear system 110 is aplanetary-type system such that the first plurality of intermediategears 112 and the first gear carrier 113 revolve about the first sungear 111, with the first ring gear 114 being static. Accordingly, thefan 142 may be mechanically coupled to the first gear carrier 113. Invarious embodiments, and with continued reference to FIG. 2B, the secondepicyclic gear system 120 is a star-type system such that the secondplurality of intermediate gears 122 and the second gear carrier 123 donot revolve around the second sun gear 121, and instead the second ringgear 124 rotates around the second sun gear 121. Accordingly, the lowpressure compressor 144 may be mechanically coupled to the second ringgear 124.

In various embodiments, the fan 142 and the low pressure compressor 144are configured to operate in the same direction. In various embodiments,the fan 142 and the low pressure compressor 144 are configured tooperate in different directions. Further, as mentioned above, not onlymay the rotational directions of the fan 142 and the low pressurecompressor 144 be different from each other, but the speeds may bedifferent from each other, and/or may be different from the speed of thelow speed spool 130 itself.

In various embodiments, the gas turbine engine 100 includes a commonstatic support structure 150 for the first and second epicyclic gearsystems 110, 120. For example, the static first ring gear 114 of thefirst epicyclic gear system may be mechanically coupled the commonstatic support structure 150 and the static second gear carrier 123 maybe mechanically coupled to the common static support structure 150. Invarious embodiments, these connections may be direct connections. Thatis, respective static portions of the first and second epicyclic gearssystems may both be directly mechanically coupled to the common staticsupport structure 150.

In various embodiments, the fan 142 and the low pressure compressor 144are both supported, using one or more bearings, against the commonstatic support structure 150. For example, the common static supportstructure 150 may be radially outward of and concentric with a shaftportion of the fan 142 and a shaft portion of the low pressurecompressor 144 may be radially outward of and concentric with the commonstatic support structure 150.

In various embodiments, the common static support structure 150 isparallel to the engine central longitudinal axis A-A′ of the gas turbineengine 100. The common static support structure 150, according tovarious embodiments and with continued reference to FIG. 2B, ismechanically mounted to a structural case (e.g., engine case 136 of FIG.2A) via support member 155. Support member 155 extend from the commonstatic support structure 150 toward a location that is aft of both thefan 142 and the low pressure compressor 144. In various embodiments,this support member 155 is positioned forward of the high pressurecompressor 152.

In various embodiments, and with reference to FIG. 3, the first sun gear311 of the first epicyclic gear system 310 and the second sun gear 321of the second epicyclic gear system 320 have different radii. Forexample, the low speed spool 330 of the gas turbine engine 300 maycomprise a common sun gear shaft 335 that comprises the first sun gear311 and the second sun gear 321, and the first sun gear 311 may have aradius that is smaller than the radius of the second sun gear 321. Invarious embodiments, both epicyclic gear systems 310, 320 areplanetary-type systems, with corresponding shaft portions of the fan 342and the low pressure compressor 344 being mechanically coupled to therespective gear carriers 313, 323. In various embodiments, both rotatingshaft portions of the fan 342 and the low pressure compressor 344 arerotatably supported, via one or more bearings, by the common staticsupport structure 350. The common static support structure 350 may bemechanically coupled directly to one of the static ring gears of theepicyclic gear systems 310, 320. In various embodiments, the commonstatic support structure 350 is coupled to the engine case via supportmember 355, which may extend between the fan 342 and the low pressurecompressor 344.

In various embodiments, the static first ring gear 314 of the firstepicyclic gear system 310 is directly mechanically coupled to the commonstatic support structure 350. In various embodiments, the static secondring gear 324 of the second epicyclic gear system 320 is mechanicallycoupled to a portion of the structural case disposed between the lowpressure compressor 344 and the high pressure compressor 352.

In various embodiments, and with reference to FIG. 4, the first sun gear411 of the first epicyclic gear system 410 and the second sun gear 421of the second epicyclic gear system 420 have the same radius. That is,the low speed spool 430 of the gas turbine engine 400 may comprise acommon sun gear shaft 435 having first and second sun gears 411, 421that have the same radius. In various embodiments, both epicyclic gearsystems 410, 420 are star-type systems having static intermediate gears412, 422 and respective gear carriers 413, 423, with corresponding shaftportions of the fan 442 and the low pressure compressor 444 beingmechanically coupled to the respective rotating ring gears 414, 424.

In various embodiments, one or both rotating shaft portions of the fan442 and the low pressure compressor 444 are rotatably supported, via oneor more bearings, by the common static support structure 450, with thecommon static support structure 450 being mechanically coupled directlyto the static gear carriers 413, 423 of the epicyclic gear systems 410,420. For example, the common static support structure 450 may extendbetween the respective gear carriers 413, 423. In various embodiments,the common static support structure 450 is coupled to the engine casevia support member 455, which may extend aft from the second epicyclicgear system 420 toward a location aft of both the fan 442 and the lowpressure compressor 444 but forward of the high pressure compressor 452.

In various embodiments, and with reference to FIG. 5, a method 590 ofoperating a gas turbine engine is provided. The method 590 may includeoperating at least one of a fan and a prop at a first operating speed atstep 592 and operating a low pressure compressor at a second operatingspeed at step 594. In such a method 590, the at least one of the fan andthe prop and the low pressure compressor are mechanically connected to alow speed spool of the gas turbine engine via a first epicyclic gearsystem and a second epicyclic gear system, respectively.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure.

The scope of the disclosure is accordingly to be limited by nothingother than the appended claims, in which reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather “one or more.” It is to be understood that unlessspecifically stated otherwise, references to “a,” “an,” and/or “the” mayinclude one or more than one and that reference to an item in thesingular may also include the item in the plural. All ranges and ratiolimits disclosed herein may be combined.

Moreover, where a phrase similar to “at least one of A, B, and C” isused in the claims, it is intended that the phrase be interpreted tomean that A alone may be present in an embodiment, B alone may bepresent in an embodiment, C alone may be present in an embodiment, orthat any combination of the elements A, B and C may be present in asingle embodiment; for example, A and B, A and C, B and C, or A and Band C. Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

The steps recited in any of the method or process descriptions may beexecuted in any order and are not necessarily limited to the orderpresented. Furthermore, any reference to singular includes pluralembodiments, and any reference to more than one component or step mayinclude a singular embodiment or step. Elements and steps in the figuresare illustrated for simplicity and clarity and have not necessarily beenrendered according to any particular sequence. For example, steps thatmay be performed concurrently or in different order are illustrated inthe figures to help to improve understanding of embodiments of thepresent disclosure.

Any reference to attached, fixed, connected or the like may includepermanent, removable, temporary, partial, full and/or any other possibleattachment option. Additionally, any reference to without contact (orsimilar phrases) may also include reduced contact or minimal contact.Surface shading lines may be used throughout the figures to denotedifferent parts or areas but not necessarily to denote the same ordifferent materials. In some cases, reference coordinates may bespecific to each figure.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,”“various embodiments,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it may be within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element is intended to invoke 35 U.S.C. 112(f)unless the element is expressly recited using the phrase “means for.” Asused herein, the terms “comprises,” “comprising,” or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus.

What is claimed is:
 1. A gas turbine engine comprising: a high speedspool mechanically connecting a high pressure turbine to a high pressurecompressor; a first epicyclic gear system; a second epicyclic gearsystem; and a low speed spool mechanically connecting a low pressureturbine to at least one of a fan and a prop via the first epicyclic gearsystem and to a low pressure compressor via the second epicyclic gearsystem.
 2. The gas turbine engine of claim 1, wherein the firstepicyclic gear system and the second epicyclic gear system comprise acommon sun gear shaft.
 3. The gas turbine engine of claim 2, wherein thecommon sun gear shaft comprises a first portion that is forward of asecond portion, wherein the first portion is mechanically connected tothe first epicyclic gear system and the second portion is mechanicallyconnected to the second epicyclic gear system.
 4. The gas turbine engineof claim 3, wherein the first portion has a different radius than thesecond portion.
 5. The gas turbine engine of claim 1, wherein the firstepicyclic gear system and the second epicyclic gear system are mountedto a common static support structure.
 6. The gas turbine engine of claim1, wherein the at least one of the fan and the prop and the low pressurecompressor are mounted to a common static support structure.
 7. The gasturbine engine of claim 1, wherein the first epicyclic gear system, thesecond epicyclic gear system, the at least one of the fan and the prop,and the low pressure compressor are mounted to a common static supportstructure.
 8. The gas turbine engine of claim 7, wherein the commonstatic support structure is parallel to an engine central longitudinalaxis of the gas turbine engine.
 9. The gas turbine engine of claim 8,wherein the common static support structure is mounted to a structuralcase aft of both the at least one of the fan and the prop and the lowpressure compressor, but forward of the high pressure compressor. 10.The gas turbine engine of claim 1, wherein the at least one of the fanand the prop is the fan, wherein the fan and the low pressure compressorare configured to rotate in a same direction.
 11. The gas turbine engineof claim 1, wherein the at least one of the fan and the prop is the fan,wherein the fan and the low pressure compressor are configured to rotatein opposite directions.
 12. The gas turbine engine of claim 1, whereinthe first epicyclic gear system is a planetary-type system.
 13. The gasturbine engine of claim 12, wherein: the at least one of the fan and theprop is the fan; the first epicyclic gear system comprises a gearcarrier mounted to intermediate gears; and the fan is coupled to thegear carrier.
 14. The gas turbine engine of claim 1, wherein the secondepicyclic gear system is a star-type system.
 15. The gas turbine engineof claim 14, wherein: the second epicyclic gear system comprises arotating ring gear; the low pressure compressor is coupled to therotating ring gear.
 16. A gas turbine engine comprising: a high speedspool mechanically connecting a high pressure turbine to a high pressurecompressor; a first epicyclic gear system; a second epicyclic gearsystem; and a low speed spool mechanically connecting a low pressureturbine to at least one of a fan and a prop via the first epicyclic gearsystem and to a low pressure compressor via the second epicyclic gearsystem; wherein the first epicyclic gear system and the second epicyclicgear system comprise a common sun gear shaft, wherein the common sungear shaft comprises a first portion that is forward of a secondportion, wherein the first portion is mechanically connected to thefirst epicyclic gear system and the second portion is mechanicallyconnected to the second epicyclic gear system.
 17. The gas turbineengine of claim 16, wherein the first epicyclic gear system and thesecond epicyclic gear system are mounted to a common static supportstructure.
 18. The gas turbine engine of claim 17, wherein the commonstatic support structure is parallel to an engine central longitudinalaxis of the gas turbine engine.
 19. The gas turbine engine of claim 18,wherein the common static support structure is mounted to a structuralcase aft of both the at least one of the fan and the prop and the lowpressure compressor, but forward of the high pressure compressor.
 20. Amethod of operating a gas turbine engine, the method comprising:operating at least one of a fan and a prop at a first operating speed;operating a low pressure compressor at a second operating speed; whereinthe at least one of the fan and the prop and the low pressure compressorare mechanically connected to a low speed spool of the gas turbineengine via a first epicyclic gear system and a second epicyclic gearsystem, respectively.